The present invention relates to the art of restraining particulates that are subject to the forces of gas or fluid flow. It finds particular application in conjunction with restraining zeolite particles in the adsorption beds of pressure swing adsorption (PSA) gas concentrators and will be described with particular reference thereto. It is to be appreciated, however, that the present invention may find utility in conjunction with other types of gas concentrators and gas concentration cycles as well as with other fluid treatment operations, such as filters, catalysts, ion exchange systems, and the like.
Heretofore, pressure swing adsorption gas concentrators have commonly included first and second molecular sieve beds connected by a cross over valve to an air compressor. The beds are filled with particles of a zeolite, carbon, or other material which adsorbed selected component(s) of the air, e.g. nitrogen, received at an input port while allowing other components, e.g. oxygen, to pass through the bed to an output port. In some concentrators, the beds have layers or strata of particulates with different characteristics.
The cross over valve cyclically supplied atmospheric air under pressure to the input port of one of the beds while purging the other bed by venting or drawing a vacuum on its input port. A small part of the separated oxygen from the output port of the bed receiving the air under pressure is fed back to the output port of the bed being purged.
These changes in pressure and flow tend to cause an unwanted movement of the zeolite particles. The movement rubs the particles together abrading them. The abrading of the particles creates smaller particles which are even more mobile, hence accelerating the abrading.
One prior art solution was to apply an axial compressive force on the cylindrical molecular sieve beds. For example, the molecular sieve bed was housed in a cylindrical housing in which one or both of the ends could be moved axially. After the bed was filled with zeolite, the ends were pressed together and locked. One of the problems with axial pressure is that the effect of the clamping force was dissipated and became ineffectual within a short distance. The particles compact into a bridge that protects interior regions from the pressure. Moreover, when the particles became smaller due to abrading, they filled voids and packed more tightly, relieving the clamping pressure. During normal use of a pressure swing adsorption system, the beds receive various thermal forces, vibration, and the like, which tend to cause undesirable movement of the particles. Moreover, the thermal expansion, the abrading and settling of particles, the introduction of compressed air, and the like tend to defeat or relieve the clamping force.
The use of spring clamping systems to apply a continuing longitudinal spring bias also tended to be ineffective. Again, the spring force was dissipated within a short distance allowing the particles at some distance from the spring to move. The particles under pressure adjacent the spring would pack together and form a bridge which blocked the spring force from reaching particles beyond the bridge from the spring. Thus, the particles at the center of the cylinder still abraded, packed together, formed voids, and thus increased the mobility of the particles.
The present invention provides a new and improved particulate anchoring system which overcomes the above referenced problems and others.